The present invention relates to measurement of acceleration corresponding to individual cylinders of an internal combustion engine, and more particularly to a method, and corresponding apparatus, for measuring acceleration corresponding to the engine individual cylinders during engine operation.
In the typical four-stroke internal combustion engine, the four strokes include the intake stroke, the compression stroke, the power stroke, and the exhaust stroke. One engine cycle is comprised of 720 degrees of crankshaft rotation during which each cylinder passes through each of its four strokes.
Gas pressure from combustion in a properly firing cylinder accelerates the engine crankshaft during the power stroke of that particular cylinder. If a cylinder fails to properly fires or produce power, then friction, compression in other cylinders, and external load combine to produce a net deceleration during the power stroke. By virtue of its mass and the arrangement of cylinders, an engine is intentionally designed to provide smooth rotation. Therefore, the speed changes resulting from the accelerations and decelerations are small compared to total rotational speed.
Recently, there is growing demand to set, as a desired air fuel ratio, a lean air fuel ratio greater than the stoichiometry air fuel ratio for idle operation at cold engine in order to suppress production of exhaust contaminants. If the lean air fuel ratio is set as the desired air fuel ratio, the engine tends to vibrate at a considerably high level, thereby considerably impairing comfortable ride feel and start-up performance. This high level of engine vibrations at idle operation attributes mainly to:
a) Combustion speed variation between cylinders due to irregularity in configuration between air intake pipes connected to the cylinders and to unevenness in intake air amount between the cylinders by intake interference, and to difference in gas flow between the cylinders; PA1 b) Difference in combustion temperature between the cylinders due to engine coolant passage, PA1 c) Dispersion in cylinder volume and piston configuration between the cylinders, PA1 d) Dispersion in air fuel ratio between the cylinders due to fuel injection amount by manufacturing tolerance of fuel injectors. PA1 a position sensor providing position signals at predetermined points of the rotation of the engine's crankshaft, said predetermined points being at regularly spaced rotation angles such that at least one position signal occurs during every power stroke; and PA1 a device, connected to said sensor, measuring a first time period of rotation through a first rotation interval defined by first selected position signals separated by a first angle of rotation and measuring a second time period of rotation through a second rotation interval defined by second selected position signals separated by a second angle of rotation, and measuring a third time period of rotation between said first and second rotation intervals, each of said first and second rotation intervals including a selected power stroke, PA1 said device calculating a first instantaneous speed as a function of said first measured time period and calculating a second instantaneous speed as a function of said second measured time period, PA1 said device calculating a ratio of the difference between said first and second calculated instantaneous speeds to said third measured time period, PA1 said device determining the acceleration based on said calculated ratio. PA1 a second sensor providing reference marker signals at second predetermined points of rotation of the engine's crankshaft, said second predetermined points being at regularly spaced rotation angles such that one reference signal occurs during every power stroke. PA1 a rotor for rotation with the crankshaft having reference marks at predetermined positions; and PA1 a stationary pickup sensing the passage of said reference marks. PA1 a rotor for rotation with the crankshaft having reference marks at predetermined positions; and PA1 a plurality of stationary pickups, each sensing the passage of said reference marks. PA1 providing position signals at predetermined points of the rotation of the engine's crankshaft, said predetermined points being at regularly spaced rotation angles such that at least one position signal occurs during every power stroke; PA1 measuring a first time period of rotation through a first rotation interval defined by first selected position signals separated by a first angle of rotation; PA1 measuring a second time period of rotation through a second rotation interval defined by second selected position signals separated by a second angle of rotation; PA1 measuring a third time period of rotation between said first and second rotation intervals, each of said first and second rotation intervals including a selected power stroke, PA1 calculating a first instantaneous speed as a function of said first measured time period; PA1 calculating a second instantaneous speed as a function of said second measured time period, PA1 calculating a ratio of the difference between said first and second calculated instantaneous speeds to said third measured time period; and PA1 determining the acceleration based on said calculated ratio.
The vibration level, during engine operation at idle, can be lowered if combustion state variations between cylinders is condensed.
U.S. Pat. No. 5,016,591 (=JP-A 2-64252) proposes an apparatus for controlling an internal combustion engine wherein crankshaft speed during the power stroke of each of the engine cylinders is detected. When the engine is idling, the average of readings of crankshaft speed of one cylinder is compared with that of the adjacent one of the other cylinders to calculate a deviation between them. Control parameters, such as basic spark timing amounts or basic fuel injection amount, on combustion within the one and the adjacent one cylinders are altered in such directions as to reduce the deviation toward zero.
According to this known apparatus, a time period of rotation through a rotation interval within each power stroke is measured. In other words, measurement of the time period or sampling is made once during each power stroke. The difference between the measured time period during one power stroke and that during the preceding power stroke is calculated for each cylinder. This calculated difference is considered as a value representative of torque produced by a particular cylinder. This value, however, results from contribution from the power stroke of one particular cylinder and that from the power stroke of another cylinder, failing to represent torque of a particular cylinder. With the same cylinder torque, the calculated difference provides different values for different engine speeds at idling. Desired idle speed gradually changes for changes in engine coolant temperature or it increases in response to application of external load by switching-on of an air conditioner of other electrical accessory.
Accordingly, an object of the present invention is to provide a method of and the corresponding apparatus for measuring acceleration corresponding to the power stroke of individual cylinders of an internal combustion engine.